The present invention is directed to plastic container closures for beverage, food, juice, pharmaceutical and like applications, and more particularly to an improved closure and method of manufacture having a sealing liner with resistance to transmission of gases (such as oxygen and carbon dioxide), water vapor and/or flavorants (flavor scalping).
It has heretofore been proposed to provide a plastic closure for a container that comprises a plastic cap or shell with an interior liner for sealing engagement with the sealing surface of the container. For example, U.S. Pat. No. 4,984,703 discloses a plastic closure that comprises a shell having a base wall with a peripheral skirt and a thread for securing the closure to a container, and a sealing liner compression molded in situ on the interior of the shell base wall. The sealing liner comprises a blend of ethylene vinyl acetate (EVA) and a thermoplastic elastomer material such as olefin or styrene-butadiene-styrene (SBS). U.S. Pat. No. 5,451,360 discloses a method and apparatus for compression molding the liner in situ within the closure shell.
Although the closures and methods of manufacture disclosed in the noted patents address problems theretofore extant in the art, further improvements remain desirable. For example, although olefin copolymers such as EVA are sufficiently resilient to provide good sealing against the sealing surface of a container when the closure is fastened to the container. these materials do not provide an acceptable barrier against transmission of gases, such as oxygen and carbon dioxide, that can deleteriously affect the product within the container. It has been proposed to employ a barrier material such as ethylene vinyl alcohol (EVOH) as a gas transmission barrier liner. However, materials of this character tend to be expensive and brittle, and are not well suited to function as a seal.
EP 0926078A1 discloses a plastic closure and method of manufacture in which the liner is compression molded in situ on the interior surface of the closure base wall, and consists essentially of a multiplicity of alternating layers of a matrix polymer and a barrier polymer to resist transmission of gas, water vapor and/or flavorants through the liner and closure. An adhesive material is provided in the liner for adhering the matrix polymer layers to the barrier polymer layers, and for adhering the liner to the closure shell, and is either blended with the matrix material or provided as separate layers between the matrix and barrier polymer layers. EVA and EVOH are preferred matrix and barrier polymers respectively. However, it has been found when implementing the teachings of this disclosure that separation and tearing can occur among the matrix and barrier polymer layers when the closure is threaded onto a container finish.
It is therefore a general object of the present invention, in accordance with one aspect of the invention, to provide a liner for a plastic closure that combines the functions of a seal for engagement with the container sealing surface and an improved barrier against gas transmission, flavor absorption (flavor scalping) and/or water vapor permeation. Another object of the present invention, in accordance with a second aspect of the invention, is to provide a barrier liner that is contoured to resist layer separation and tearing as the closure is applied to a container finish.
A plastic closure in accordance with one aspect of the present invention includes a closure shell having a base wall, a peripheral skirt with an internal thread or bead for securing the closure to a container finish, and an internal annular lip extending from the shell skirt adjacent to the base wall and defining an inside lip surface at an acute angle to the shell base wall. A liner is compression molded in situ onto the base wall and peripherally within the lip. The liner has a liner base portion extending along the shell base wall and a peripheral portion extending along the inside surface of the lip. The liner has an interior surfacexe2x80x94i.e., facing away from the shell base wall and skirtxe2x80x94that has a first flat axially facing portion on the base portion of the liner adjacent to the peripheral portion, an inwardly concave portion where the base portion blends into the peripheral portion of the liner, a second flat axially facing portion at an edge of the concave surface portion of the liner, and a conical portion that extends from a radially outer edge of the second flat portion to the inside surface of the lip. Provision of the second flat axially facing surface portion at the periphery of the liner has been found to reduce tearing of the liner and separation of layers in the liner, when the liner is of layered construction in accordance with a second aspect of the invention, as the closure is threaded onto a container finish.
In accordance with a second aspect of the invention, which preferably is used in combination with but may be implemented separately from other aspects of the invention, the liner is compression molded in situ on the base wall of the closure, and consists essentially of alternating layers of EVA matrix polymer, adhesive polymer and EVOH barrier polymer to resist transmission of gases, water vapor and flavorants through the liner and the closure. The EVA matrix polymer is preferably selected from the group consisting of EVA and EVA blends, specifically a melt blend of EVA and styrene-ethylene-butylene-styrene (SEBS).